The subject matter of this invention relates generally to programmable controller systems and relates more specifically to failure indicators for the same.
Programmable controller systems in general are well known. Examples of such systems may be found in the Westinghouse Descriptive Bulletin 16-354 entitled "Numa-Logic.TM.700 and 900 Series Programmable Controllers", Apr. 4, 1983 and Descriptive Bulletin 16-355 entitled "Numa-Logic.TM.PC-1100 Programmable Controller", April 1983, both of which were published by the Westinghouse Electric Corporation (Industry Electronics Division), the assignee of the present invention. Generally, programmable controller systems of the type mentioned include a basic central processing unit which includes a microprocessor, power supply apparatus, and a databus. The CPU is typically usable with some form of programming device, e.g. a keyboard which may be disconnectably connected thereto for programming. Input/output cards are provided for utilization with the central processing unit for taking addressed data from the central processing unit and using that data to drive load devices such as relays and the like. Input/output cards may also perform input functions for the central processing unit, that is provide information about machine status to the central processing unit for subsequent utilization by the central processing unit for control of machine functions. An auxiliary peripheral cathode ray tube may be utilized, for example, in the programming operation for the programmable controller. The Programmable controller operates automatically to control relays, solenoids and other output devices in correspondence with predetermined program conditions, feedback from the devices and operating conditions associated with the devices.
Programmable controller systems usually have associated therewith indicating devices such as light emitting diodes or the like for providing an indication of the status of certain operations, or apparatus within the programmable controller. It would be desirable to provide an indicating device on an output card which provides an indication if an important portion of the electronic circuitry of the output card fails or is shorted out while the card is in place on line, in a real time operating situation in a card rack so that appropriate action can be manually or otherwise taken to safeguard the status of the load served by the card in question. It would be desirable if this could take place whether the load served thereby was in a non-energized or OFF state or in an energized or ON state. This would be especially helpful where the logic transfer elements within the card ceased to operate to pass logic signals within the card or if there was failure of an output switch.